Finish Design/stateful NAT64

doc/Design.tex

@@ -231,17 +231,33 @@ entries for translating from IPv4 to IPv6. Our P4/BMV2 offers the
 highest degree of flexibility, as it provides support for invidual
 entries based on table entries and LPM table entries.
 % ----------------------------------------------------------------------
-\section{\label{design:statefulnat64}Stateful NAT64 - FIXME: write}
-- controller selects "outgoing" IPv4 address range => base for sessions
-- IPv4 addresses can be "random" (in our test case), but need
-to be unique
-- switch does not need to know about the "range", only about
-sessions
-- on session create, controller selects "random" ip (ring?)
-- on session create, controller selects "random port" (next in range?)
-- on session create controller adds choice into 2 tables:
-incoming, outgoing
-
+\section{\label{design:statefulnat64}Stateful NAT64}
+Similar to stateless NAT64, the design of stateful NAT64 depends on
+the features of the invidual implementation. As pointed out in section
+\ref{background:transition:statefulnat64}, stateful NAT64 is very
+similar to stateless NAT64, with the main difference being an
+additional stateful table that helps to create 1:n mappings.
+We use different approaches within the implementations
+to solve this problem:
+\begin{itemize}
+\item For P4/BMV2 and P4/NetPFGA a python controller handles packets
+  that don't have a table entry, sets the table entry in the P4 switch
+  and inserts the original packet afterwards back into the switch.
+\item With tayga we rely on the Linux kernel NAT44 capabilities
+\item Jool implements its own stateful mechanism based on a port
+  ranges
+\end{itemize}
+All methods though operate in a very similar fashion: A ``controller''
+inspects the IPv6 packet and depending on the source address,
+destination address, protocol (TCP, UDP,
+ICMP, ICMP6, etc.) and the protocol ID (source / destination TCP/UDP
+port, ICMP identifier) it selects an outgoing IPv4 address, and source
+port or ICMP identifier.
+In case of Jool and Tayga this decision is based on a session table
+inside the Linux kernel, in case of P4 this decision is based on a
+session table inside the python controller. While the Jool and Tayga
+both support cleaning up old session entries,
+our P4 based solution does not support this feature at the moment.
 % ----------------------------------------------------------------------
 \section{\label{Design:BMV2}BMV2}
 Development of the thesis took place on a software emulated switch